1. Field of the Invention
This invention deals with the art of vision correction through the application of a soft contact lens to the human eye. More particularly, details a novel method to dynamically altering the optical power of a soft contact lens, while in the eye, through gaze dependent use of fluid dynamics.
2. Description of the Prior Art
The human eye contains two main tissues or elements that act to focus light onto the retina. The cornea, which is the clear, watch crystal like tissue on the outside of the eye, focuses light coming from distant objects. The ability to see distant objects is referred to herein as distant vision.
The other tissue or element is the crystalline lens on the inside of the eye (i.e., disposed radially inwardly from cornea) that performs the focusing necessary to clearly image objects closer than approximately 20 feet, herein after referred to as near objects or near vision. The lens consists of concentric layers of protein arranged like an onion. As a person ages the lens gradually thickens and becomes less pliable. By the age of around 40, many people experience a condition known as of presbyopia or the inability for focus that results from this thickening of the lens.
Historically, presbyopia has been addressed with spectacle lenses or glasses. These glasses are available in two forms: with reading lenses and with multifocal lenses. Reading glasses are appropriate to correct near vision. Their disadvantage is that a wearer must remove them in order to see clearly at distance. Glasses with multifocal lenses, including bifocals and progressive, address both distance and near vision. These types of lenses have lens portions with different focal points. Generally in a bifocal the top portion of the lens is adapted to provide distance vision while the bottom portion near vision. The person wearing the glasses holds their head so that they can gaze through the top portion to see far objects. In order to see at near they would keep their head as if they were looking at a distance then rotate their eyes downward so that they can gaze through the bottom portion in order to clearly focus on near objects. Multifocal lenses, like trifocals and progressive, have several additional portions to provide accurate focusing for objects at various intermediate distances from a wearer.
Some forty years ago, contact lenses (or contacts) started to be used as a common alternative to glasses to address both distance and near blurred vision. Two types of contact lenses are presently in use: Rigid Gas Permeable or Hard contact lenses, (herein referred to as just hard lenses) and soft contact lenses. Hard contact lenses to correct distance vision generally are fit to partially rest up under the upper lid and move with the lid during the blink. Translating bifocal hard contact lenses work somewhat differently in that the lower edge of the contact rests against the lower lid so that as the wearer looks from a distant to a near object the lens stays stationary at the lower lid as the eye rotates downward so as to be looking through the near vision portion of the contact.
Soft contact lenses on the other hand drape on the cornea like a wet tee shirt and therefore remain essentially in the same location with respect to the optical axis of the eye even during the blink.
This presents a problem when one wants to create a bifocal soft contact lens because, no matter the direction of gaze, the visual axis of the eye always passes through the same portion of the lens. This problem is currently addressed by creating a contact that contains multiple refractive surfaces disposed directly along the visual axis. Examples of designs used for this purpose include aspheric, diffractive, concentric power rings, and refractive islands. Unfortunately all of these designs focus light coming from different distances onto the retina simultaneously. As one could imagine these designs result in “double or triple exposures” on the retina and significantly degrade the quality of the retinal image.
It is for this reason that development of a better soft bifocal contact lens is important.